grease pencil rig+ stroke getting messed up
From a quick glance it looks like you've assigned the same vertex to multiple bones so you're getting multiple movements.Try assigning the hand just to the hand bone and remove from the arm etc.
From my experience with Grease Pencil weight painting seems to only apply a 1 or 0 in 2D as opposed to actual weights unfortunately (I'm currently in an experimental build so may just be the version I'm in).
Hope that helps
Matt